NAME

       PCRE2 - Perl-compatible regular expressions (revised API)

SIZE AND OTHER LIMITATIONS

       There are some size limitations in PCRE2 but it is hoped that they will never in practice be relevant.

       The maximum size of a compiled pattern is approximately 64K code units for the 8-bit and 16-bit libraries
       if PCRE2 is compiled with the default internal linkage size, which is 2 bytes for these libraries. If you
       want  to  process  regular  expressions  that  are truly enormous, you can compile PCRE2 with an internal
       linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded up to 4). See the README  file  in
       the  source  distribution  and  the  pcre2build  documentation  for  details. In these cases the limit is
       substantially larger.  However, the speed of execution is slower. In the  32-bit  library,  the  internal
       linkage size is always 4.

       The  maximum  length  of  a  source  pattern  string is essentially unlimited; it is the largest number a
       PCRE2_SIZE variable can hold. However, the program that  calls  pcre2_compile()  can  specify  a  smaller
       limit.

       The  maximum  length (in code units) of a subject string is one less than the largest number a PCRE2_SIZE
       variable can hold. PCRE2_SIZE is an unsigned integer type, usually defined as size_t. Its  maximum  value
       (that  is  ~(PCRE2_SIZE)0)  is  reserved  as  a  special  indicator for zero-terminated strings and unset
       offsets.

       All values in repeating quantifiers must be less than 65536.

       The maximum length of a lookbehind assertion is 65535 characters.

       There is no limit to the number of parenthesized subpatterns,  but  there  can  be  no  more  than  65535
       capturing subpatterns. There is, however, a limit to the depth of nesting of parenthesized subpatterns of
       all kinds. This is imposed in order to limit the amount of system stack used at compile time. The default
       limit  can  be  specified when PCRE2 is built; the default default is 250. An application can change this
       limit by calling pcre2_set_parens_nest_limit() to set the limit in a compile context.

       The maximum length of name for a named subpattern is 32 code units,  and  the  maximum  number  of  named
       subpatterns is 10000.

       The  maximum  length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb is 255 code units for the
       8-bit library and 65535 code units for the 16-bit and 32-bit libraries.

       The maximum length of a string argument to a callout is the largest number a 32-bit unsigned integer  can
       hold.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge, England.

REVISION

       Last updated: 30 March 2017
       Copyright (c) 1997-2017 University of Cambridge.